Tsunami 

A tsunami is a series of waves generated by the sudden movement of the ground at a location beneath a water body (for example, in the ocean or a lake) and rapid displacement of the water above it.

Tsunamis are often caused by large undersea earthquakes, but can also be triggered by submarine landslides, volcanic eruptions and even large meteorite impacts. In a large tsunami, a series of waves may arrive over several hours with significant time between the wave crests. The first wave to reach the shore may not be the largest.

Tsunamis can range in height from as little a few centimetres to tens of metres in size and travel at great speeds (400-700 kph). They can transport huge volumes of water and travel many kilometres inland. They can cause significant flooding of low-lying areas, serious damage to property and infrastructure and pose a considerable danger to people.

We have modelled the tsunami flood hazard extent for 17 places along the Otago coast, as part of work carried out by NIWA for ORC in 2007. Mapped hazard areas show the extent of flooding specific communities might see under three credible tsunami scenarios:

• A tsunami originating from an earthquake in South America, with an estimated return period of 500 years.
• A more likely tsunami originating from an earthquake in South America, with an estimated return period of 100 years.
• A tsunami originating from an earthquake on the Puysegur Trench to the south of New Zealand, with an estimated return period of 600 years.

Other settlements and unpopulated stretches of the Otago coast are also subject to tsunami hazard, but we do not yet have sufficient information to model tsunami in these locations.

Please visit the Coastal Hazards tab in the Otago Natural Hazards Database Portal to see and explore the mapped hazard extents for tsunami from the 2007 report.

Alternatively, please read the 2007 Tsunami modelling study and/or visit the publications and reports section on our website for more technical report information on coastal hazards in Otago.

The Otago Civil Defence and Emergency Management has information about how to prepare for a tsunami.

Glossary

Tsunami return period: Estimated time between tsunami events of a certain size.